Automatic disconnect system



Dec. m, was. .1. MESZ'AR mzswa AUTOMATIC DISCONNECT SYSTEM Filed Feb. 28, 1935 lNl ENTOR J. MESZA R Patented Dec. 10, 1935 UNITED STATES ATENT OFFICE AUTOMATIC DISCONNECT SYSTEM Application February 28, 1935, Serial No. 8,593

6 Claims.

This invention relates to trunk circuits arranged to instantaneously disconnect the talking conductors from the inward or plug end of the trunk when the calling or outward end is released prior to disconnection of the trunk plug from the called line.

In systems of this character it has been the practice to operate a disconnect relay at the inward, end when the outward end of the trunk is released thereby opening the trunk conductors at that point. Further, in order to completely free the called line so that it can be taken for use by another operator before the trunk plug is removed from the line, the disconnect relay causes the normal sleeve relay circuit of the trunk, which is of relatively low resistance, to be disconnected and substitutes a high resistance relay therefor which causes the sleeve relay in the line to release thereby causing the line to test idle and making it available for another call. In such an arrangement the high resistance relay in the trunk sleeve operates and holds the disconnect relay operated thereby preventing a recall on the trunk from releasing the disconnect relay and reconnecting the trunk through to the called line. When the trunk plug is removed from the called line the trunk circuit restores to normal.

An arrangement of this character is satisfactory in cases where the sleeve circuit of the called line is not employed for other purposes, i. e., when other sensitive relays are not connected thereto which, however, is the case with certain modern toll lines in which various unrelated functions are controlled over the sleeve circuit thereof by means of sensitive apparatus operated by current supplied to the sleeve of the line from a connected cord or trunk.

In such cases to effectively free the line it would be necessary, with the previous circuits, to employ a relay of such high resistance that the current would be of such a low value as to preclude its satisfactory operation.

An object of the present invention, therefore, is to effectively free the connected line, when the outward end of the trunk is released, and prevent its reconnection to the trunk before the trunk plug is disconnected therefrom without interfering with circuit devices or apparatus connected associated with that of that line.

A feature of the invention whereby the foregoing object is attained resides in the provision of a gas-filled discharge device connected to the ring of the trunk plug in such a manner that it is held inactive while the plug is connected to the line, but will discharge and cause the release of the (Cl. l7951) locked-in trunk disconnect apparatus and restoration of the trunk circuit to normal when the trunk plug is removed from the connected line.

The invention will be understood from the following description when read in connection with the accompanying drawing, which shows a one- 1' y tandem trunk circuit T, arranged according o the invention and extending between two toll itchboards, one of whichswitchboard CLR, .2 indicated at the left of the drawing with part 10 a cord circuit I and a trunk jack 2. The other apparatus of the drawing is associated with a Tandem switchboard TAN at which trunk T terminates in plug 3, which has access to a jack 4 outgoing straight forward toll line 26. When operator CLR'withdraws plug I from jack 2 at the end of a conversation between subscribers, relay 5 is caused to immediately release due to the operation of. relay 6, which locks up under control of relay 1,, which relay also operates at 2 this time. The tip and ring conductors of. the trunk are disconnected from plug 3 by the release of relay 5, and the sleeve conductor is disconnected by the operation of relay 7, thereby making the trunk T immediately available for another call at switchboard CLR, and causing straight forward toll line 26 to be indicated as idle at switchboard TAN.

According to a particular feature of the invention, when the operator TAN finally withdraws plug 3 from jack 4, the ionic tube 8 functions to. cause the release of relays l and 6, thereby restoring the trunk circuit to normal. A more complete understanding of the operation of the invention may be obtained from the following detailed description.

Assume that the operator CLR at a toll switchboard, which is of the type known in the art as a combined line and recording switchboard has received a request from a calling subscriber over a trunk circuit (not shown) for a call requiring for its completion a connection to the straight forward toll line 26, the conductors of which terminate on the jack 4. The operator CLR will now insert plug 9 into jack 2, thereby operating sleeve relay ll! over a circuit traced from battery through the winding of cord circuit sleeve relay l l, sleeve contacts of plug 9 and jack 2 and winding of relay iii to ground. Relay ii! in operating, operates relay I2 through a circuit including battery, the

winding of relay l2, outside normally closed contacts of relay I3, and ground on the outside operated mate contacts of relay l0. Relay i2 in operating alsooperates relay l 5 through a circuit from battery on the inner operated make conhasbeen connected,'inserts plug 3 into straight fforward toll line jack 4,;thereby operating relay I5 to ground on the contacts of relay I2. Relay I5 in operating, operates relay I6 through a circuit from battery through the winding of relay I6, right-hand operated makercontacts of relay I5,

7 and lamp I4 to ground. Relay I6 in operating operates through an obvious circuit relay I I, which in operating connects battery to the upp r terminal of relay I6. This short-'circuitsthe winding of relay I6 and applies full battery potential to lamp' I4 over the circuit hereinbefore traced. Lamp 14 now lights and relay I6 by reason of the application of the aforesaidshort V clusion of the resistance of the winding of relay It in its energizing circuit and relay I6 reoperates over the circuit hereinbefore traced, due to the 'removal'of the shortcircuit appliedby the contacts of relay IT. The cycle of operation and release of relays I6 and I1 is repeated causing the flashingof lamp I4. r 7

When relay I5 operated it also connected, at its left-hand contacts, the tip and ring conductors, I8 and I 9, to the operators telephone and control circuit of the tandem switchboard, which is indicated diagrammatically by a rectangle 20. It should be explained here that the relays l2 and I5 represent the 'so-called sequence relays of a system of automatic listening, whereby the trunks of a trunk switchboard position are connected one at a time, in sequential order, to the operators telephone circuit of the trunk position.

As this system iswell-known in the art, and is unnecessary. for a description of the present invention, it is not shown here. It should be un-,

derstood, accordingly, that the tandem trunk circuit T illustrated in thedrawing is one of a number of trunks and that when relay I5 eflectedits aforesaid connection to the operators telephone ,7

TAN. I Operator CLR now requests connection to the toll line. terminating in'jack 4. 'The operator TAN observing that the flashing lamp I4 is associated with trunk T, which identifies the trunk towhich her telephone and control circuit 2| over a circuit traceable from battery through the windings of relays 2i and 22, normally closed contacts of relay 1, sleeve contacts of plug 3 and jack 4, through left-handhigh resistance winding of 1:01 meisleev 'relay 23 and other appa 'ratus' not shown, to ground. 7

Relay22 being marginal does not operate 'cu'itQ'indicated but not shown in detail, to cause the transmission of a ringing signal toward the 7 office of the called subscriberfand also to operate operate which in turn connects ground to circuit in this circuit but relay 23 operates and closes a cirtacts ofrelay I0, through the winding of relay sistance 30 through its own contact and contacts 3| and 32 of relay 5, which relay is operated at this time as hereinafter described. Relay 23 in operating also closes a circuit to display a busy signal 29. Resistance 30 is now connected in shuntwith the winding of relay I0 thereby lowering the sleeve resistance to ground of jack 2 and plug 9 and causing a supervisory lamp (not shown) associated with cord circuit I to light.

When relay 2I operated it caused the operation of relay 5 over a circuit that may be traced from battery through the winding of relay 5, right-hand normally closed contacts of relay 6 to ground on the contacts of relay 2i. Relay 5 in operating connects tip and ring conductors I8 and I9 to corresponding conductors 26 and thereby completing a conversational path to the straightforward toll line 26. Relay 5 also operates relay 13 from battery on the inner front contact of relay I0 through the winding of relay I3 to ground on contact spring 28 of relay 5. Relay I3 in operating opens at its normally closed contacts the operating circuit hereinbefore traced for relay I2 which relay now releases. The release of relay I2 opens the obvious operating circuit of. relay I5 I3 to ground on the outer operated contacts of When the operator at the distant completing central oflice is connected to the toll line 26, establishes the desired connection to the called subscrib'ers line and the called subscriber answers by removing his receiver from the switchhook;'apparatus (not shown) associated with the outward end of the line 26 atthe TAN operators position functions to release relay 56 thereby opening the low resistance sleeve circuit previously'mentioned through the right-hand winding of relay 23 thus increasing the resistance of the sleevecircuit of jack 4. Under this high resistance condition marginal relay 22 in the cord circuit releases and in so doing disconnects ground from resistance 3& causing thereby an increase in resistance of the sleeve circuit of jack 2, which causes the supervisory lamp (not shown) of cord circuit I to be extinguished thereby indicating to the CLR operator that the called subscriber'has answered.

At the end of the conversation when the called subscriber replaces his receiver on the switchhook' relay 4% is again caused to operate, thereby shunting the left-hand high resistance winding of relay 23 by the low resistance circuit through its right-hand winding which as before described will cause reoperation of marginal relay 22 in the cord circuit which, in turn, reconnects resistance to ground and reduces the resistance of the sleeve circuit of jack 2 to cause the lighting of the supervisory lamp of cord circuit I all as hereinbefore described in connection with the insertion of plug 3 into jack 4 on originating the -a disconnect signal and withdraws plug 9 from 'jack2. 'This opens the circuit of relay lfi, which releasescausing the release of relay i3 and the pperation: of relay 6 over a circuit that may be traced from battery through the back contacts of relay l0, left-hand normally closed contacts and winding of relay 6 to ground on the operated contacts of relay 2i. Relay 7 also operates at this time through a circuit traceable from battery on the back contacts of relay H3, through left-hand normally closed contacts of relay 6, left-hand windingof relay '5, to ground on the operated contacts of relay 2%.

In operating, relay 1 looks to ground onits lefthand outer make contacts, being energized by battery on the left-hand, inner operated contacts of relay 6, and also opens the sleeve circuit of plug 3 and jack 4. Relays 2 l, 22 and 23 release, and lamp 29 is extinguished. It will be noted here, that the left-hand contacts of relay '5 are arranged so that the outside contacts close, before the inside contacts break, thereby assuring that relays 6 and l are held operated before the operating circuit of relay 2| is opened which relay in releasing disconnects the original operating ground for relays 6 and 1. Relay 5 in operating, locks to battery on its left-hand inner make contacts and to ground at the left-hand contacts of relay 1 and opens at its right-hand contacts the operating circuit, hereinbefcre traced, of relay 5 which releases, breaking the continuity of the talking contactors, opening the circuit of resistance 35!, removing ground from the winding of relay 5%, which releases and closes its own lowermost contacts. It will be noted that straightforward toll line 25, although plug 3 is still in jack 3, is now available through multiple jacks (not shown) for another call, since the tip and sleeve conductors of plug 3 are open, while the ring conductor is connected to ground and battery through very high resistances 38, 39 and 40.

When relay 5 operated it also closed a circuit for lighting lamp M as a disconnect signal for the attention of the operator TAN. This circuit may be traced from ground through lamp id, outer left-hand operated contacts of relay 6 to battery on the back contacts of relay l0.

Let it be assumed now that, before the operator TAN responds to the lighted disconnect lamp Hi, by withdrawing plug 3 from jack 4 that this trunk is reselected by the same CLR operator or by another CLR operator having access to trunk T. Relays ii 62 and it will again operate, as hereinbefore described. Relay l5 will reconnect operators telephone and control circuit 29 to the talking conductors and lamp 5 4 to the flashing relays Iii and I1. Lamp Hi again flashes and order tone is again heard by operators CLR and TAN as in the case of the original call. The operator CLR now requests that a connection be completed by operator TAN, who observes the dashing lamp i i and knows thereby that it is the plugged up trunk that has been selected. Operator TAN now removes the trunk plug 3 from jack =3 and the feature of this invention will now be described whereby the release of relays 5 and i from their interlocked condition hereinbefore described is effected.

When relay '1 operated and locked to ground on its outer left-hand contacts through its lefthand winding it also prepared a circuit for its right-hand winding that may be traced from battery 34 through right-hand inner contacts of relay 1 to anode 35 of gaseous discharge tube 3, thence through tube 8 to its cathode element 36 and the right-hand winding of relay 7 to ground. Another circuit was closed by the right-hand inside contacts of relay '5 which may be traced from battery 34, junction point 37, through high resistances 38 and 39 to ground. Relay 1.! also connects junction point 42, between resistances 39 and 46, to the ring conductor of thecord and toll line, which is grounded through a relay ll whose function is to control ringing over the line. It should be observed. that grid element 43 of tube 8 is also connected to junction point Under the circuit condition hereinbefore described tube 8 does not discharge and there is no current flow through the right-hand winding of relay l, since the potential of grid element is insufficient to effect the ionization of tube 8. When plug 3 is removed from jack 4, the circuit traced through the winding of relay il is opened and consequently the current flow therethrough due to the potentialof junction point 52 ceases. The effect of this is to decrease the current flow in resistance 38, which raises the positive potential of junction point 42 and consequently of grid element 43, sufficiently to cause the ionization and discharge of tube 8. Consequently, current now flows from battery 34 and between electrodes 35 and 36 of tube 8 through the right-hand winding of relay 7, hereinbefore referred to. The righthand winding of relay l is so connected that, when energized by the ionization current of tube 8 as hereinbefore described, it opposes the magnetic action of its left-hand winding and this opposing action is sufiicient to cause the relay to release. When relay 1 releases ground on its left-hand contacts is removed from the winding of relay 5, which also releases, thereby the trunk available for the new call.

Due to the extremely rapid functioning of tube 8 after grid 43 has reached the ionization potential it has been found desirable to retard the establishment of said ionization potential for the reasons hereinafter given. When relay "5 operates there is a possibility that the necessary ionization potential may be established on grid 43 by the closure of the right-hand inner contacts of relay 1, before the current in resistance 40 has reached its final maximum value following the closure of the right-hand cuter contacts of that relay, thereby causing a premature release of relay 1. The desired retardation is obtained by the time required to charge condenser 44 which is connected in parallel with resistance 39, since the potential of grid 53 cannot reach its final maximum value until condenser 2 is completely charged.

In connection with the foregoing description it should be stated that the resistances 33, 39, and 48 used in association with the ionic tube 8 are all of a very high order of resistance. has been found that a suitable resistance value for resistance 38 is of the order of Z megohms, for resistance 39, 5 megohms and for resistance 40, 1 megohm. Accordingly, the connection of conductor 45, with its associated apparatus, to ring conductor 25 can have no effect on the transmission of voice currents, ,nor interfere in any manner with the proper functioning of relays in the straightforward toll line circuit, or other associated circuits. Also, because of this high resistance, there is no interference with the use of straightforward toll line 26, if this line is reselected for use before plug 3 is withdrawn from jack 4.

The arrangement of the invention that has been described refers specifically to means for effecting the release of certain relays in a trunk circuit by the use of an associated control circuit of very high resistance, including an ionic tube, which functions, when the trunk is disconnected from an associated line to cause the tube to discharge and effect the release of the certain relays. It' is to be understood, however, that the invention is also applicable to other circuit conditions, especially to cases where it is essential that the resistance of said control circuit, which may be used to effect the release of relays or perform some other desirable circuit function, shall be of a very high order, avoiding thereby any disturbing effects on transmission or on the performance of associated relays or other circuit apparatus. These other applications will readily occur to one skilled in the art.

What is claimed is: i

1. In a telephone system, a trunk line having outward and inward ends, means for establishing a connection with the trunk line at the outward end, an outgoing line at the inward end, means for connecting said'trunk line to the outgoing line, a guard signal associated with the inward end 7 of said trunk line, means automatically responsive to the release of the trunk line at the outward end while the inward end is connected to the outgoingline to open the talking conductors of the trunk at the inward end, and display said guard signal, and a gas-filled discharge 'device' associated with the inward end of said trunk line responsive-to the disconnectionof said trunk line from the outgoing line for retiring said guard signal. 7

2. In a telephone system, a calling line 'termicalled line and responsive to disconnection of the plug from the called line to unlock said first and second means. I

3. In a telephone system, an outward switchboard, an inward switchboard, a trunk line therebetween, an established connection to said line at the outward board, an outgoing line at the inward board, a plug terminating the inward end of said trunk line and connected to said outgoing line, means responsive to the release of the trunk connection at the outward switchboard for disconnecting said trunk line from the plug at the inward board, a second means also responsive to the release of the trunk connection at the out ward board for establishing a locking circuit for itself and the first means, and means including a gas-filled discharge device maintained inert over a circuit including thering conductors 'of the plug and connected to the outgoing line adapted to cause the release of said first and sec-. ond means when the connection between said plug and outgoing line broken.

4. In a telephone system, a trunk line having outward and inward ends, a toll line, means for establishing a connection with the trunk line at the outward end thereof, means for establishing a connection between the trunk line and the toll line at the inward end of the trunk line, means at the inward end of the trunk line jointly responsive to disconnection from the trunk line at the outwardend and to the connection of the trunk line to the toll line to open the trunk line conductors at the inward end, means at the inward end of the trunk line for locking operated the last-mentioned means independent of the connection to the trunk line at the outward end,

' and an ionic tube at the inward end of the trunk line for efiecting the release of said locked means, said ionic tube functioning in response to the disconnection of the trunk line from the toll line.

5. In a telephone system, a line having outward and inward ends, means for establishing a con- 3,

end and means for effecting the release of said line opening means by causing the ionization of said ionic tube by an increase in potential on said grid element in response to the disestablishmerit of the connection at the inward end.

6. In a telephone system, a line having outward and inward ends, means for establishing connection with the line at the outward end, means for establishing connection with the line at the inward end, means for opening the line conductors at the inward end responsive to the disestablishment of the connection at the outward end, means for causing said line opening means to be locked operated independent of the connection at the outward end, an ionic tube at the inward end having anode, cathode and grid elements, a relay winding in series with said anode and cathode elements, means for connecting a source of potential in series therewith responsive to the said disconnection at the outward end, other means similarly responsive to the disconnection aforesaid to cause a gradual establishment of a potential on said grid element below the ionization potential of said ionic tube, and means responsive to the disestablishment of the connection at the inward end whereby the potential of said grid element is increased so as to effect the ionization and discharge of said ionic tube to cause a flow of current through the circuit of said relay winding to cause its operation and the release of said locked line opening means.

JOHN MESZAR. 

